Improvements to decimal conversion#292
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…ues (e.g., Decimal256 with precision 76, scale 38) that previously threw OverflowException — addresses issue apache#247 - Adds a fast path using Int128 on .NET 7+ that avoids BigInteger allocation for values that fit in 128 bits - Replaces the old fractional-part overflow check (which threw) with FractionToDecimal, which gracefully reduces precision to fit within decimal's ~28-digit mantissa
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Pull request overview
This PR improves decimal conversion for Arrow decimal arrays, fixing high-scale conversion overflows (notably Decimal256 precision 76 / scale 38) and adding a .NET 7+ fast path to reduce BigInteger allocations.
Changes:
- Fixes
DecimalUtility.GetDecimalto handle high-scale values more gracefully by reducing fractional precision instead of throwing. - Adds a .NET 7+ (
net8.0in this repo)Int128-based conversion fast path for 128-bit values (and 256-bit values that sign-extend into 128 bits). - Expands test coverage for high-precision/scale
GetValueand introduces a new benchmark for decimal access patterns.
Reviewed changes
Copilot reviewed 7 out of 8 changed files in this pull request and generated 5 comments.
Show a summary per file
| File | Description |
|---|---|
| src/Apache.Arrow/DecimalUtility.cs | Adds Int128 fast path and replaces fractional overflow throwing with truncation-based conversion. |
| src/Apache.Arrow/Arrays/Decimal128Array.cs | Adds TryGetValue convenience API for decimal retrieval. |
| src/Apache.Arrow/Arrays/Decimal256Array.cs | Adds TryGetValue convenience API for decimal retrieval. |
| test/Apache.Arrow.Tests/DecimalUtilityTests.cs | Updates expectations so high-scale Decimal256 conversion no longer throws. |
| test/Apache.Arrow.Tests/Decimal128ArrayTests.cs | Adds high-scale GetValue/TryGetValue tests for Decimal128. |
| test/Apache.Arrow.Tests/Decimal256ArrayTests.cs | Adds high-scale GetValue/TryGetValue tests for Decimal256 (issue #247 scenario). |
| test/Apache.Arrow.Benchmarks/DecimalArrayBenchmark.cs | Adds new BenchmarkDotNet benchmarks for decimal conversions/accessors. |
| .gitignore | Ignores BenchmarkDotNet output artifacts. |
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… the `TryGetValue` path.
adamreeve
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Mar 24, 2026
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adamreeve
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adamreeve
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Looks good thanks Curt, I just have some minor suggestions
adamreeve
approved these changes
Mar 25, 2026
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What's Changed
Closes #247.
Partially addresses #96.